Chairs for a draftsman usually provide an elevated seat so that as the draftsman works at a drafting table from the elevated seat his legs are unable to reach to the floor. A footrest is provided for the draftsman's comfort and is adjustable vertically along the support column of the chair to a location most comfortable for the legs of the draftsman.
Prior proposed devices for retaining such a footrest at a selected height included set screws or devices which contacted and applied a holding force directly to the support column or to an intermediate sleevelike bushing encircling the column. The support column was often a pneumatic cylinder which facilitated changing the elevation of the chair. Applying a set screw or clamping force to a pressure area of very small area concentrated the pressure and sometimes caused distortion of the column which resulted in malfunctioning of the pneumatic cylinder. When the set screw or clamping force was applied to an intermediate bushing, a sufficient tightening force was difficut to achieve and slipping of the footrest downwardly would often occur when the draftsman's weight was placed on the footrest. Thus, positive retention and positioning of the footrest at a desired height was difficult to consistently achieve and such prior devices often resulted in damage to the support column of the chair.